Share thisThe evolution of caging systems over recent decades has run parallel to changes in the requirements coming from academic institutions and the research industry
The original need to have just a "container" for rodents used in research, made of any cheap material like wood, has developed over time into the need to meet a whole host of practical, scientific requirements. These include: health status, bio-containment or bio-exclusion, separation of small groups of animals, space saving, ergonomics, practicality of use, and last but not least, animal and human welfare.
The development of static micro-isolators was certainly the first step toward achieving the goal of increased protection for animals and humans. But even when considering that different micro-isolators can have different performances in terms of gases accumulation1in relation with the size of the filter surface, it was very clear from the beginning of their use, that a once or twice a week frequency of bedding change was the limiting factor. Humidity, temperature, and CO2 and NH3 concentrations were also a matter of concern. Furthermore, the use of paper filters with poorly defined porosity and degree of protection given to the content of the cage led to the development of ventilated cabinets to hold micro-isolators with the double aim of giving relief to the microenvironment and improving the bio-exclusion and bio-containment performances.
Micro-isolators and ventilated cabinets were successful formany years, but limitations due to cage density per square foot became a serious matter of concern when, more recently, the extraordinary development and diffusion of transgenic mice colonies and immuno-deficient strains highlighted the need for technical solutions where a combination of priorities like cage density, animal welfare, bio-exclusion, and bio-containment are a must.
The state of the art in terms of caging systems for rodents is represented by modern Individually Ventilated Cages (IVCs). Some fundamental features pertaining to performance standards of such equipment have been deeply investigated by various authors over the years in order to understand the possible effects of the caging environment, not only on the physiology and behavior of mice, but also on the working environment of people. A number of questions on IVC technology have been posed by animal care specialists and investigators. They refer mainly to the need to understand the possible effects on animal welfare and physiology due to the key differential feature between old traditional caging systems (open cages, static micro-isolators) and IVCs: forced intra-cage ventilation. How should so large a volume of High Efficiency Particulate Air (HEPA) be pushed and moved inside each single cage in order to avoid stress, ensure efficient gas removal, and as a consequence, create an improved, stable microenvironment that allows the expression of natural and physiological behaviors in rodents? Is it possible to define the "best"? operating mode for the ventilation of an IVC in terms of intra-cage airflow, air speed etc. in order to leverage all the advantages and remove the disadvantages of this peculiar ventilated enclosure?